Volga State University of Water Transport

About: Volga State University of Water Transport is a education organization based out in Nizhny Novgorod, Russia. It is known for research contribution in the topics: Attractor & Creep. The organization has 71 authors who have published 75 publications receiving 224 citations.

Modeling fatigue life of polycrystalline structural alloys under a combined effect of low- and high-cycle fatigue mechanisms

Abstract: Processes of fatigue life of polycrystalline structural alloys under a combined effect of low- and high-cycle fatigue are considered. In the framework of mechanics of damaged media (MDM), a mathematical model is developed, which describes processes of plastic deformation and fatigue damage accumulation. The MDM model consists of three interrelated parts: relations defining cyclic elastoplastic behavior of the material, accounting for its dependence on the failure process; equations describing fatigue damage accumulation kinetics; a strength criterion of the damaged material. The version of defining relations of elastoplasticity is based on the notion of yield surface and the principle of orthogonality of the plastic strain rate vector to the yield surface at the loading point. This version of equations of state reflects the main effects of the cyclic plastic deformation process of the material for arbitrarily complex loading trajectories. The version of kinetic equations of damage accumulation is based on introducing a scalar parameter of damage degree. The construction uses energy-based principles and accounts for the main effects of the process of nucleation, growth and merging of microdefects under arbitrarily complex multiaxial loading regimes. A combined form of the evolutionary equation of fatigue damage accumulation in the regions of low-cycle (LCF) and high-cycle (HCF) fatigue is proposed. It is shown that, under regular cyclic loading of the material, the stress amplitude of the cycle decreases by degrees during the transition from LCF to HCF and depends on the physical interaction of these mechanisms in the transition zone. The condition when the damage degree attains its critical value is taken as the strength criterion of the damaged material. A methodology of numerically determining parameters of the evolutionary equation of fatigue damage accumulation in the conditions of HCF is presented. To assess the reliability and the limits of applicability of the defining relations of MDM, processes of plastic deformation and fatigue damage accumulation in a number of structural alloys in cyclic tests have been numerically studied, and the obtained numerical results have been compared with the data of full-scale experiments. The results of comparison of the numerical and experimental data reveal that the developed model of mechanics of damaged media adequately describes durability of structures subjected to a combined effect of low- and high-cycle fatigue mechanisms. It is shown that the introduced MDM model qualitatively and, accurately enough for practical engineering purposes, quantitatively describes the main effects of the processes of plastic deformation and fatigue damage accumulation in structural alloys under cyclic loading.

Modeling transient processes of diesel-generator set with variable rotation frequency on the basis of active voltage rectifier

Abstract: The variants of transformerless power topologies of ship diesel generator sets of variable rotational speed are considered. A power circuit of a diesel generator set of variable rotational speed on the basis of an active voltage rectifier and a buffer energy store, which has the highest efficiency in terms of weight and size and performance, is proposed. A block diagram of a control system for semiconductor converters as part of a diesel generator set of variable rotational speed is presented. The control system of the active voltage rectifier is implemented upon the principle of regulation according to the position of the generalized voltage vector of the network. In order to increase the energy efficiency of the inverter diesel generator set there has been developed the algorithm for smooth control of the rotational speed of the internal combustion engine using setting mechanism of suspend mode. The proposed algorithm (gradient descent method) is borrowed from the neural network technologies and allows calculating the rotation frequency of the internal combustion engine shaft corresponding to the minimum specific fuel consumption when operating at the current fractional load. In MatLab Simulink computer environment a simulation model of a variable-frequency diesel generator set based on active voltage rectifier was developed and transients were studied. The results of simulation modeling of the dynamic modes of the load switching have been presented, taking into account its size and nature; the indicators of the specific fuel consumption of the internal combustion engine as part of a diesel generator set of variable rotational speed are presented, as well. Using a variable-speed diesel generator set based on an active voltage rectifier has been proved to allow ensuring the required quality indicators of the generated electricity when the internal combustion engine is operating at lower energy-efficient rotation frequencies in the fractional load mode.

On possibility of remote detection of gas leaks from underwater pipelines using specific slick signatures

Abstract: One of the urgent problems of gas pipeline transport today is the detection of gas leaks in underwater sections of gas pipelines and reducing their negative impact on the environment. This paper is devoted to the development of remote detection methods of gas leaks from underwater gas pipelines by images of slicks above them. A series of laboratory experiments was carried out, in which the structure of average flows in the water column created by bubble flows with different gas flow rates was obtained. The simulation of surfactant removal to the water surface by bubbles was performed by adding sodium dodecyl sulfate (SDS) to the laboratory cuvette at the concentration of 0.5 mg/l. For the surfactant film on the water surface, experimental dependences of its characteristics on the operation time of the "bubble pump", such as the surface tension coefficient, elasticity and the relative damping coefficient of small- scale waves under the film, were obtained. It was shown that there are flow convergence zones at some distance from the gas outlet area, which vary depending on the intensity of the gas flow. Surfactant film samples taken in these areas confirmed that over time, the accumulation of surfactants occurs on the water surface. Field experiment conducted in one of the backwaters of the Oka river in the city of Nizhny Novgorod allowed to spot and evaluate the size and shape of the film slick formed around the gas outlet area. The conducted experiments confirmed the formation of a surfactant film spot near the removal area, which indicates the possibility of its remote detection in full-scale conditions, provided the wind near water surface is not more than 2-10 m/s. The obtained data made it possible to get a general idea of the morphology and characteristics of the surfactant spot around the gas outlet from the water.

Information Aspects in the Field of Modern Public Administration and Law

Abstract: The authors analyzed a set of aspects related to the improvement of the sphere of public administration through the implementation of programs for the digitalization of the socioeconomic sphere of modern society. The use of modern information and telecommunication technologies, including to ensure a high level of security of citizens and the quality of life, the ability to effectively protect their interests and rights, minimize various technological and social risks, allows you to quickly solve current problems, contributes to the achievement of relevant local and global goals, both in the current conditions and in the future. The article presents and analyses relevant statistics, as well as conclusions on the stable correlation between the level of security of the population, ensuring basic constitutional rights and freedoms and the intensity of the use of means of obtaining, storing, processing and displaying information, various automated control systems and databases in the field of social management and law.